Sputtering system

ABSTRACT

A system (10) for the vacuum processing of substrates such as semiconductor wafers which includes a central handling chamber (14), a number of separately pumped and randomly accessed process chambers (16-19), and dual load lock chambers (22) which communicate with the central handling chamber. This configuration permits one batch of substrates to be subjected to load lock evacuation while a second batch, having been previously evacuated, is transferred one at a time to selected process chambers. Substrate transfer from the load locks to the central handling chamber is by means of elevators (42) and by means of a handling assembly (24) which undergoes and Z motion only, with final transfer from the central handling chamber to the process chambers being accomplished by pivoting platen assemblies (66).

This is a continuation of copending application Ser. No. 07/264,571filed on Oct. 31, 1988.

The present invention relates to the coating of thin substrates undervacuum, and more particularly to a modular sputtering system which iscapable of sputter coating substrates either serially or in a selectiveaccess sequence.

In the fabrication of relatively small disk shaped objects, such assemiconductor wafers or data storage disks, multi-layered coatings mustbe applied to their surfaces in order to achieve certain properties orobjectives. For semiconductor wafers a multi-layered conductive coatingserves to provide electrical contact to the active portions of thecircuit i.e., the resistors, capacitors, diodes and transistors, andfurther serves to interconnect these to provide a functional circuit.For a data disk, the multi-layered coating may consist of a magneticlayer for data storage and an overlayer to provide protection for thestorage layer. The apparatus used to achieve such coatings havetraditionally been classified into two types; batch coaters and singlesubstrate coaters. Batch coaters process a multiplicity of substrates ina single coating operation whereas single substrate coaters sequentiallyProcess individual substrates one at a time. This invention relatesspecifically to the achievement of multi-layered sputter coatings wherethe individual substrates are sequentially coated.

The sputter coating process requires an environment wherein a gas or gasmixture is maintained at a sub-atmospheric pressure. This gas isfrequently argon which is preferred because of its chemical inertnessand low cost, but gas mixtures may be used. For this reason, the coatingapparatus must be capable of maintaining a sub-atmospheric pressure oftypically 1 to 30 millitorr pressure, where atmospheric pressure is 760Torr. Since residual atmospheric gases such as oxygen, nitrogen andwater vapor can react with and contaminate the freshly depositedcoating, the chambers which make up a sputter coating apparatus must beevacuated by means of a pumping system such that chamber atmospheric gaspartial pressures of 10⁻⁷ Torr are routinely achievable, prior to thecoating process, and maintained during the coating process as well asduring the time interval between layer depositions. Finally, sincedifferent sputter coating process require different gas pressures or gasmixtures, it is desirable that some means be provided for achieving thisdiversity of process environments without cross-contamination.

One means of achieving these conditions is to configure the sputtercoating apparatus with a central evacuated substrate handling or stagingchamber with a valved means of accessing multiple process chambers, aswell as a vacuum load-locked means of transporting wafers to and fromthe ambient environment. While such systems are commercially availablethere are several problems associated with such systems.

In a typical state-of-the-art system substrates are processed in agenerally cylindrical central substrate handling chamber which iscontinuously evacuated by means of a vacuum pump. Surrounding thecentral substrate handling chamber are separately pumped processchambers and a separately pumped load lock. Interior to the centralsubstrate handling chamber is a substrate handling robot which iscapable of three degrees of motion, radial (R), circumferential (θ) andvertical (Z). The processing of substrates is accomplished in thefollowing steps. First, the interior hermetic door which is capable ofisolating the handling chamber from the load lock chamber is closed andlock vented to the atmosphere. Following this, the exterior hermeticdoor is opened to admit either a single substrate or a multiple-piecebatch of substrates separately racked in a standard plastic cassette orthe like. Thereafter, the outer hermetic door is closed and the loadlock chamber evacuated until a predetermined degree of lock chamberevacuation is achieved, whereupon the inner hermetic door is opened toprovide substrate access by the three-axis central substrate handler. Asingle substrate is extracted from the rack by an outward radialtraverse of the robot arm. This places the substrate pick-up end of thewafer handler arm between adjacent substrates on the rack. A shortupward Z traverse then lifts the substrate off its edge supports and thesubsequent radial retraction of the robot arm carries the wafer to aposition interior to the central substrate handling chamber. From thisposition, a θ motion allows the substrate to be carried to a positionwhere it is aligned with a slot-shaped access port to a process chamber.A hinged hermetic door separating the process and central chamber thenopens to allow radial extension of the substrate handler arm and theaccompanying thrust of the substrate into the process chamber. Thesubsequent downward Z motion places the wafer on edge supports and thesubsequent retraction of the substrate handler arm allows for thereclosing of the process chamber door and the hermetic isolation of thesubstrate in the separately pumped process chamber. The repetition ofthe above described actions allows for the sequential placement of thesubstrate in any one or all of the process chambers, thus allowing forsequential deposition of different layers without interlayer exposure tothe atmosphere. Upon completion of the coating process, the substrate isreturned to its position in the load lock rack which then allows for theeventual vent back and return to the atmosphere of the entire rack-fullof coated substrates.

One disadvantage inherent in the configuration is the fact that the loadlock evacuation occurs serially with respect to the coating process.Thus, any lengthening of the load lock cycle which may be required forminimization of particulate contamination, or minimization of residualgas transfer to the central substrate handling chamber carries with itthe penalty of reduced productivity. Related to this is the similarrestriction that the time constraints and engineering limitations do notpermit the batch heating of the substrates in the lock. This limits theeffective removal of adsorbed contaminants from the substrate surfaceprior to its introduction into the contamination sensitive portions ofthe coating apparatus. Thus a high level of contamination can find itsway into the coating process.

Another disadvantage of this configuration has to do with the increasedmechanical complexity introduced by the requirement that the centralwafer handling robot have a radial motion capability. This requirementintroduces the need for mechanisms and bearings to be present in thevacuum environment of the central substrate handling chamber wherecontamination considerations do not permit the use of lubricants.Accordingly, these mechanisms become prone to the generation ofparticulate contamination which if allowed to settle on the substratesurface will result in the unacceptable generation of coating defects.Similarly, these mechanisms are also prone to vibration which thenimplies the need for some type of edge contact with the substrate inorder to maintain substrate placement accuracy. For silicon wafersubstrates, such edge contact is a known source of particulatecontamination.

A further disadvantage of the previously described configuration isassociated with the relatively large process chamber volume which isrequired by the need to provide rotational means inside this chamber forplacing the substrate in a vertical attitude. This increased processchamber volume results in a lengthening of the evacuation time neededbefore the substrate can be transferred back into the central waferhandling chamber without substantial risk of contamination. This needfor increased dwell time in the process chamber reduces the productivityof the coating apparatus. Similarly, the larger relative volume ofprocess to central handling chambers, implies a higher level of centralhandling chamber contamination at the chosen degree of process chamberevacuation where substrate transfer is carried out. This results fromthe fact that gaseous contaminants experience a dilution upon migratingfrom the process to the central handling chamber, which dilutiondecreases as the process chamber is made large relative to the centralhandling chamber. For both these above reasons, an apparatusconfiguration having large process chambers has a higher potential forresidual gas cross-contamination.

To overcome the above shortcomings the present invention provides acentral substrate handling or staging chamber with separately pumpedprocess chambers, and dual load lock chambers which are alternatelyloaded with multiple-piece substrate batches (25 pieces being a standardbatch of semiconductor wafers), using an external substrate handlingrobot. Accordingly, while one substrate batch is undergoing load lockevacuation, the second batch, having been previously evacuated, isaccessible to the central wafer handling robot for purposes of executionof the coating process. For this reason, load lock dwell times areordered parallel to the coating process and extended load lock dwelltimes do not impair apparatus productivity until the batch lock dwelltime exceeds that time needed for the serial coating of a full batch ofindividual substrates. The benefit of this increased permissible lockdwell time is enhanced by the provision of means for heating thesubstrate batch. Thus, batch evacuation and thermal desorption are bothaccomplished before the opening of the interior load lock door whichindividually opens a given lock chamber to the central handling chamber.

Upon completion of this lock cycle, the opening of the interior lockchamber door allows the substrate rack to be accessed by a substratehandling robot located inside the separately pumped central waferhandling chamber. In accordance with the invention the wafer handlingrobot is provided with only a circumferential (θ) and vertical (Z)translation capability. Accordingly, the previously described pick-upand place action permits individual substrates to be extracted from themetal rack, carried along the circular path and placed down on a seriesof two-position platens located on the circular path. Once the substratehas been transferred and the wafer handler moved away, a clamp isactivated to cause the substrate to be held near its edge and pressedagainst the platen surface. Thereupon, the platen is caused to pivot90°. This action causes the substrate to be placed vertically andthrusts it through a large opening in the central wafer handlingchamber. Located opposite this opening is the sputtering source,hermetically mounted to the exterior wall of a separately pumped processchamber. This previously described pivoting motion also causes ahermetic seal to be effected between the platen housing and the interiorwall of the central substrate handling chamber. This seal, located atthe periphery of the large circular opening in the central substratehandling chamber, effectively isolates the process chamber from thecentral substrate handling chamber. Once this seal has beenaccomplished, the previously described sequence of sputter gasintroduction, and application of sputtering source power, causes thesubstrate to become coated. Similarly, post-deposition re-evacuation ofthe process chamber, and the subsequent reverse pivot of the substrateplaten opens the interchamber seal, and allows the unclamping andtransfer of the substrate to another platen where the entire process isrepeated to cause a second sputter-deposited layer to cover the first.By repetition of this action the substrates can be sequentially carriedthrough a series of isolated process chambers where any desiredcombination of coating and etching operations may be performed. Once anentire batch has been sequentially processed and returned to the loadlock rack, the load lock is sealed, vented back to atmospheric pressure,and the batch returned to the original plastic cassette from whence ithad been extracted.

In addition to the dual batch load lock configuration, thisconfiguration has the following advantages. (A) the central waferhandling robot, having no radial motion mechanism is capable of verysmooth particulate free wafer transfer; (B) the individual processchambers are much smaller permitting much more rapid, contamination-freetransfer of wafers through the sequences leading to the multi-layeredsubstrate coating; and (C) the combination of this serial coatingprocessing with parallel batch lock operation uniquely achieves a veryhigh level of purity with regard to residual atmospheric gases.

Other advantages of the invention will be apparent from the followingdescription when considered in connection with the accompanyingdrawings, wherein:

FIG. 1 is a perspective view of the sputtering system of the invention,with portions removed or cut away for clarity;

FIG. 2 is an elevation view, with parts cut away, of the load locks ofthe invention;

FIG. 3 is a sectional view of the wafer handling assembly of theinvention;

FIG. 4 is a sectional view taken along line 4--4 of FIG. 3.

FIG. 5 is a sectional view of the wafer handling arm of the invention;

FIG. 6 is a plan view of the wafer handling arm;

FIG. 7 is a view, shown partly in section of a platen assembly of theinvention;

FIG. 8 is a plan view of the platen assembly;

FIG. 9 is a sectional view taken along line 9--9 of FIG. 8;

FIG. 10 is a rear elevation view of a platen assembly with parts shownin section to illustrate an atmospheric clamp assembly of the invention;

FIG. 11 is a schematic side elevation view of the platen assemblypositioned at a process chamber;

FIG. 12 is a fragmentary sectional view of a clamp assembly of theinvention; and

FIG. 13 is a fragmentary view along line 13--13 of FIG. 12.

Referring to FIG. 1, there is illustrated a sputtering system,designated generally by the numeral 10, which includes a loading station12 at atmospheric pressure, an evacuated central handling or stagingchamber 14, a plurality of evacuated process chambers 16, 17, 18, 19 and20, first and second load lock chambers 22 located between the stagingchamber and the loading station, and a wafer handling assembling 24located within the staging chamber. A top plate and removable cover (notshown) are received over the staging chamber to enclose the chamber forvacuum processing. For purposes of illustration herein the substrates tobe sputtered will be described as semiconductor wafers, although it willbe understood that the present invention can be used to coat other formsof substrates such as audio discs.

LOADING STATION

In accordance with a preferred embodiment of the invention the loadingstation comprises a platform 26 which receives four standard wafercassettes 28 loaded with wafers 30, a flat finding station 32 whichpre-orients each wafer with the flat in a predetermined angularposition, and a handling assembly 34. As illustrated herein the handlingassembly 34 comprises a platform 35 which is movable along rails 36extending along the open faces of the cassettes 28, and an articulatedwafer picking arm 37 mounted on the platform 35; however, it can beappreciated that a multi-axis robot system can also be used. Thecomponents of the loading station are well-known and commerciallyavailable items, and will not be described in further detail herein.

LOAD LOCKS

The load locks 22 are identical and are described interchangeablyherein. In FIG. 2, the load locks are viewed from inside the stagingchamber 14. Referring to FIGS. 1 and 2, the load lock 22 is a two-levelstructure including an upper level 38 having an access door 39 facingthe loading station and a lower level 40 opening into the stagingchamber 14 to provide access to the wafers 30 by the wafer handlingassembly 24. Within the load lock there is mounted a rack 41 whichincludes a plurality of spaced-apart metallic wafer supporting elements.Each rack holds a standard cassette-load of twenty-five wafers and isreceived on an elevator 42 which is operable to position the rack at theupper level 39 to receive wafers transferred from the cassettes by thearm 37, and to move it downward to the lower level 40 in position to beaccessed by the handling assembly 24. To maintain the vacuum integrityof the chamber 14 when an elevator is in the up position as shown on theleft side of FIG. 2, the base 44 of each of the rack/elevator assemblies41 defines a valve element which is operable to seal the opening betweenthe upper and lower levels of the load lock.

The elevator actuating mechanism 46 is mounted below the chamber 14, anda bellows 47 surrounds the actuating shaft of the elevator to preventvacuum loss. A poppet valve unit 48 is mounted atop the chamber and hasa valve element 49 which is operable to open and close a port 50 betweenthe chamber 22 and an upper plenum 51. A cryogenic pump 52 operates toevacuate the plenum 51 and chambers 22, while a poppet valve 53 controlsthe inlet to the pump.

Also mounted within the load lock chambers 22 are radiant heating units45 disposed vertically on opposite sides of the rack 41. Preferably theheating units comprise a plurality of quartz halogen heating lamps suchas those manufactured by USHIO INC. and designated as series QIR. When arack is fully loaded and the load lock closed and evacuated, the heatersare effective to remove adsorbed contaminants from the wafer surfacesprior to the entry of the wafers into the staging chamber 14.

In operation, a cassette-load of wafers 30 is transferred,one-at-a-time, from one of the cassettes 28, to the flat-finder 32 andthen to the rack 41 by means of the wafer handling assembly 34. The door39 is then closed and the chamber partially evacuated using a mechanicalroughing pump (not shown). One of the valves 49 is then opened andcryogenic pump 52 is activated to evacuate the open load lock 22 to apressure approaching that of the chamber 14. Valve 53, shown in the openposition in FIG. 2, is provided to close the inlet to the pump 52 formaintenance and regeneration of the pump. The heaters 45 are thenenergized to effect a batch degassing of the wafers. The valve 49 isthen closed and the elevator 42 is moved downward to the position shownon the right side of FIG. 2, the downward movement opening the valveelement 44 and thus opening communication between the right side loadlock 22 and the staging chamber 14. At this point a rack load of wafersare in position to be accessed by the wafer handling assembly 24 as willbe described in more detail below.

As noted above, the plenum 51 communicates with both load locks 22 theloading, evacuating, heating and transfer functions for both of the loadlocks being essentially the same as that described above.

STAGING CHAMBER

Referring to FIG. 1, the staging chamber 14 is essentially octagonal inplan view with three sides of the octagon cut off by the plane definedby the face of the load lock chamber. The bottom of the staging chamberis a plate 54 with a plurality of wells 56 formed therein arranged in acircular pattern about an axis defined by the axis of the handlingassembly 24. The side walls 60 define interfaces between the stagingchamber and the individual process chambers 16-20, and the top of thechamber is defined by a readily opened and removable cover, which is notshown herein in the interest of clarity.

Each of the chambers 16-20 could be used to perform any one of a numberof different processes such as etching, or sputter coating. For example,a plasma etch unit 61 can be installed at chamber 16 and sputter sources62 and 63 installed at process chambers 17 and 18, with chamber 19having another sputter source (not visible) and chamber 20 being used asa vacuum pump station, with a vacuum pump 65 installed therein. It canbe appreciated, however, that with relatively little modificationchamber 20 could be employed as a sputtering or other processing stationwith the vacuum pump communicating with the staging chamber through, forexample, the bottom plate 54.

Within each of the wells 56, there is mounted a platen assembly 66(shown schematically in FIG. 1), which is pivotable from a wafertransfer position shown in solid line in FIG. 1, to an operatingposition shown in broken line only at process station 18. As will bediscussed in detail below, the platen serves both as means for retainingwafers and as a valve for isolating the process chamber from the stagingchamber when the wafers are being processed, or when a particularprocess chamber is undergoing maintenance.

Wafers are transferred between the load locks 22 and the processchambers 16-19, or from one of the process chambers to any one of theother process chambers by means of the wafer handling assembly 24.

WAFER HANDLING ASSEMBLY

Referring to FIGS. 3 and 4, there is illustrated the wafer handlingassembly 24, comprising a mounting flange assembly 68 received in anopening 70 formed through the bottom plate 54 of the staging chamber, asupport plate 72 attached to and depending from the flange assembly, alead screw linear drive system supported by the plate 72 and designatedgenerally by the numeral 74, a drive shaft assembly 76 mounted on thedrive system for linear movement i.e. the required Z axis movement ofthe handling assembly, a rotary drive system 78 mounted on the shaftassembly to provide the (θ) movement of the handling assembly, and ahandling arm 80 attached to the shaft assembly and adapted to receivewafers for transfer to and from the process stations and the load locks.

The support plate 72 is essentially a channel as shown in plan view inFIG. 4, to which the movable elements of the wafer handling assembly aremounted, including the linear drive system 74 and the rotary driveSystem 76.

The linear drive assembly 74 comprises a housing 82, also in the form ofa channel, which supports the drive shaft assembly 76 and the drivesystem 78, pairs of bearing carriers 83, and 84 attached to the housing,a pair of rails 85 and 86 attached to the plate 72 on which the bearingcarriers are supported, and a lead screw drive assembly designatedgenerally by the numeral 88.

The bearing carriers 83-84 enclose low-friction linear bearings whichride on the rails 86. The lead screw drive assembly 88 comprises upperand lower spacers 89 and 90 attached to the plate 72, a lead screw 92mounted for rotation in the spacers, a lead nut assembly 94 attached tothe housing 82, and a drive system 96. The lead nut assembly 94comprises a support block 98 fixed to the housing 82 and attached to alead nut unit 100 of the ball screw assembly. As is well known in theart, rotation of the lead screw 92 within the lead nut assembly 94,causes the housing 82 to move up or down along the rails 85, 86depending on the direction of rotation of the screw. Rotation of thelead screw 92 is provided by a motor and gear unit 102, mounted on asupport bracket 101 attached to the plate 72, which drives the screw bymeans of a timing belt 104. A brake 105 fixed to the plate 72 andoperating on the lead screw 92 maintains the position of the lineardrive system in the event of a loss of power. A shaft encoder 103, alsodriven by the motor 102 provides Z motion information to a controlsystem for the handling assembly.

The rotary drive system 78 comprises a drive motor 106 supported by aplate 107 welded to the housing 82, an output shaft 108 coupled to themotor output shaft, a rotary seal assembly 110 surrounding the shaft108, a bellows assembly 111, and the handling arm 80 attached to the endof the output shaft.

A cylindrical housing 112 depends from the motor 106, and a brake 114,similar to the brake 105, is mounted on the housing and is coupled tothe motor output shaft. A shaft encoder 116 also driven by the motor 106is mounted on the housing 112 to provide motion information to thecontrol system.

Since the area above the plate 54 is under vacuum, the sealing of thedrive assembly to prevent vacuum loss, and to avoid contamination of thehandling chamber is very important. To this end the rotary seal assembly110 provides a highly reliable means to isolate the rotating componentsfrom the vacuum system, while the bellows eliminates the need forsliding seals. The rotary seal is preferrably a type of seal referred toas FERROFLUIDIC, which is a registered trademark of FERROFLUIDICSCORPORATION, which is well known in the art and will not be described indetail herein. As illustrated in the preferred embodiment shown in FIG.3. The rotary seal is enclosed within a cylindrical housing 124 which issuspended from an end member 125 of housing 82 and sealed thereagainstby means of an O-ring 126. The housing 124 includes an elongatedcylindrical extension 128 which supports the output shaft 108 through alower bearing 129 and an upper bearing (not shown) within an end cap 130of the housing 124.

As illustrated in FIG. 3, the handling assembly must undergo significantvertical or Z axis travel in order for the handling assembly to access afull cassette load of wafers positioned on the racks 41. To accommodatethis motion without employing sliding seals, the sealed bellows assembly111 is installed between the drive system housing 82 and the plate 54which defines the floor of vacuum chamber 14. The bellows assemblycomprises an upper flange 132 which is attached to the top member of theflange assembly 68 and sealed thereagainst by an O-ring 133, a lowerflange 134 attached to the end member 125 of the housing 82 and sealedby an O-ring 135, and a metallic bellows 136 which surrounds theextended portion 128 of the rotary seal assembly 116 and is fixed to theflanges 132 and 134 by welding or brazing or the like.

Referring to FIGS. 5 and 6, the wafer handling arm 80 is a fabricatedstructured comprising a hub assembly 138 an arm structure 140 and awafer-receiving paddle 142. The hub assembly comprises a substantiallyrectangular housing 143 with a downwardly projecting hub 144 which fitsover the end of shaft 108 and is attached thereto by means of a key 145and a yoke clamp member 146 which is received in an opening formed inthe housing and includes a portion partly encircling the shaft. Theclamp member is attached to the housing by means of screws 147 (one oftwo shown). An O-ring 148 is received in a groove formed in the housingand seals against the shaft 108. A cover 149 bolted to the housingcloses the upper end of the housing and is sealed thereagainst by anO-ring 157 received in an oval groove formed in the housing.

The arm 140 is a fabricated metal box, rectangular in cross-section,which is welded to the housing 143. The outer end of the arm is weldedto an end cap 155 to which the paddle 142 is bolted. Referringparticularly to FIG. 6, the paddle 142 is a relatively thin,substantially solid member which is bolted to the end cap 155. The freeend of the paddle is formed with arms 150 and 151 with the wafers 30(shown in broken line in FIG. 6) being supported on three contact points152 distributed about a centerpoint 153 on the longitudinal axis of thearm assembly. The paddle is relatively thin, as noted above, to enablethe paddle to fit between wafers in the racks 41, and as shown in FIG. 6the paddle is offset from the centerline of the arm assembly tofacilitate entry of the paddle into the platen assemblies as will becomemore apparent from the description below. It should be noted that thewafers are maintained on the arm by gravitational force only, with noother restraint.

The paddle 142 includes three capacitive proximity sensors 154 which arereceived in depressions formed in the bottom surface of the paddle anddistributed 120° apart at a radial location corresponding to the edge ofa wafer. The sensors protrude above the top surface of the paddle andabove the pins 152. A fourth sensor 154a is centrally located and isflush to the top surface of the paddle. These sensors can be of a typemanufactured by Cox Engineering Company and designated as Model SR2 andwill not be described herein in detail. The central sensor serves todetect the presence of a wafer on the paddle and the outer sensors sensethe position thereon. A slight deviation from the position shown in FIG.6 wherein the edge of the wafer approaches within a set distance of thethree outer sensors will be detected so that misalignment and potentialdamage of the wafers when they are placed on a platen assembly can beavoided.

The sensors 154 and 154a indicate wafer position by producing a voltagelevel change in a binary manner, i.e. high voltage at sensor 154aindicates that a wafer is present; whereas a low voltage indicates nowafer. Similarly, low voltage at all three of the edge detectors 154indicates that the wafer edge is in the proper location; whereas, highvoltage at any sensor indicates that the wafer is approaching the sensorand is not in proper position. After a wafer is received on the paddleboth a wafer presence and proper wafer position signals must be receivedbefore the arm is moved. If the wafer is tipped in any direction the 20,wafer presence sensor 154a will provide a proper signal, and a waferpresence signal will be issued. If the presence condition is satisfiedbut the wafer does not lie within the three sensors 154, the wafer willbe returned to its present status, the arm will be repositioned in adirection dependant upon which of the three sensors failed to providethe proper signal, and the wafer will be lifted again to go throughanother position sensing sequence. If proper positioning is sensed thepaddle will be moved to transfer the wafer to its next station. If aftera second try proper positioning cannot be established manualintervention will be required to resolve the error.

It can be appreciated that the insertion of electrical components suchas the sensors 154 into the vacuum system can cause problems,particularly in association with a rotating component such as the armassembly 80. In accordance with the invention the electrical lines forthe capacitive sensors, collectively designated 156, are routed toconnecting points below the staging chamber through the center of thehollow shaft 108, into the housing 143, through connector block 158 andconnectors within the housing, and then through the arm 140 to thepaddle 142 where they extend through sealed openings and are receivedwithin channels formed in the underside of the paddle. As describedabove, the area below the plate 54, including the interior of the shaft108 are at atmospheric pressure; however, the O-rings 148 and 157, andan O-ring 159 between the end cap 155 and the paddle, along with thesealed openings in the paddle, maintain the integrity of the vacuumwithin the chamber 14.

In operation, the handling assembly is initially positioned adjacent toa rack 41 within one of the load locks 22. Then the motor/gear unit 102is energized to rotate the lead screw 92 and drive the housing 82 upwardto position the arm assembly 80 vertically in position such that thewafer paddle 142 is slightly below a selected wafer within the rack 41.The rotary drive motor 106 is then energized to rotate the arm until thepaddle is aligned beneath its selected wafer. The linear drive system isagain actuated to raise the arm slightly to engage the wafer with thecontact points 152. The arm is then rotated out of the load lock andlowered to the FIG. 3 position, after which the rotary drive system isagain energized to rotate the paddle to a position over any one of theplatens 66 to deposit the wafer thereon for processing, as will bedescribed in detail below.

PLATEN

Referring particularly to FIGS. 7, 8 and 9, there is illustrated theplaten assembly 66 of the invention. In accordance with the inventionthe platen assembly comprises an essentially enclosed housing 162, apivot assembly 164 attached to the end of the housing, and a platen 166.

The housing 162 comprises an upper support plate 168, a support ring 170welded to an arcuate member 171 which in turn is welded to the uppersupport plate, a lower support plate 172 which can be integral with theupper plate, a lower ring 174 welded to the plate 172 and a side wallmember 176 which encircles the rings 170 and 174 and is welded thereto,and which extends outward from the ring members to cover the open sidesbetween the support plates 168 and 172, to which it is also welded. Acylindrical cover 178, including a disk 179, a tube 180 welded to thedisk, and a ring 181 welded to the tube; is bolted to the ring 174.

The pivot assembly 164 comprises an elongated housing 182 (see FIG. 10)bolted to the ends of the support plates 168 and 170, hollow stub shafts184 welded to the housing and extending through seal and bearing units160 received in the well structure 56 the seals preferably beingFERROFLUIDIC seals. The well structure is in the form of a first sealedbox structure 161 having the rounded-end rectangular shape illustratedin FIG. 1, with a secondary cylindrical box structure 163 attachedthereto to provide clearance for the bottom portion of the platenassembly. The bearing units 160 extend through the sides of the firstbox structure 161, and one of the stub shafts is connected to a drivesystem designated 165 which can be in the form of air cylinder and leverarm system as shown schematically in FIG. 10, and which is operable tomove the platen between its horizontal loading position and its verticaloperating position.

Referring particular to FIGS. 7, 8 and 9, the platen 166 comprises anannular frame member 186 which is fastened to the ring 170 by means ofscrews (not shown), a wafer support assembly 190 clamped to the framemember 186, and a wafer clamp assembly 192 supported by the frame member186 and movable relative thereto to selectively clamp a wafer to thesupport assembly 190 and to release it therefrom.

The wafer support assembly 190 comprises a relatively thick, essentiallysolid circular platen element 194; a lower ring member 196 spaced fromthe platen 194; a relatively thin, tubular member 198 connecting theplaten 194 and ring 196 and welded thereto; and a clamp ring 200 whichis fastened to the ring 196 by screws 201 and which clamps the wafersupport assembly 190 to an inwardly projecting flange portion of thelower ring 196 through insulating rings 199.

A circular plate member 202 is fastened to the bottom of ring 196 andsubstantially closes the bottom of the support assembly 190. The plate202 has an annular channel 203 formed therein which is closed by a ring204 to define an annular cooling water channel.

An electrical resistance heater unit 208 is fastened to the platen 194by a bolt/spring washer assembly 211 and includes a circular heatingelement 209 in contact with the platen 194. A temperature probe 210 isreceived through the heating element 208 and is imbedded in the platen194 just below the wafer receiving surface. A gas line 212 is receivedthrough the plate 202 and extends through the platen 194 to communicatewith one or more channels 214 formed in the surface of the platen tosupply gas to effect gas conduction cooling of a wafer 30 received onthe support assembly. The remaining volume between the platen 194 andthe plate 202 is filled with a thermal insulating material 216.

WAFER CLAMP

Referring to FIGS. 8 and 9, wafers 30 are retained on the platenassembly for processing by a clamp system mounted on the platen. Theclamp system comprises an annular actuating cylinder assembly 222supported by the frame member 186, and the clamp assembly 192, which issupported by the frame and actuated by the cylinder assembly 222.

The cylinder assembly comprises an annular member 226 attached to theframe member 186 by bolts 227, and having an annular recess formedtherein to define a fluid cylinder 228. A sealed cover member 230 coversthe open end of the cylindrical member 226 and is fastened thereto bythe bolts 227 to sealingly enclose the cylinder 228. An annular piston232 is received within the cylinder 228 and is sealed therein by innerand outer O-rings 233 and 234. Looking at the right side of FIG. 9,there is illustrated one of three piston rod assemblies 236 attached tothe annular piston 233. The piston rod assembly comprises a rod 238extending through the piston and the cover member 230 and press fit tothe piston. The shaft is sealed at the lower end of the cylinder by anO-ring 239 retained in place by a bearing cap 240 which aligns andsupports the lower end of the piston rod, and at its upper end by anO-ring received in an insert 242 retained by a bearing cap 244 capturedbetween the cylinder 226 and the frame member. An O-ring 245 provides astatic seal between the cap and the frame.

The upper end of the shaft 238 has a reduced diameter portion which isreceived through a disc 248 and through an insulating ring 246 attachedto the clamp assembly 192, the ring and disk being clamped between theshoulder formed by the reduced diameter portion of the shaft and awasher/nut assembly threaded onto the end of the shaft. A bellowsassembly comprising the disc 248, the cap 244 and a metallic bellows 250brazed or otherwise attached to the disc and cap maintains vacuumintegrity. Fluid inlets (not shown) above and below the piston 232permit the entry of fluid pressure to the cylinder 228 to selectivelymove the rod 238 up or down to actuate the clamp assembly.

The clamp assembly 192 surrounds the platen 194 and comprises an upperring 251 and a lower ring 252 maintained in spaced relation to eachother by three spring members 254 distributed about the clamp assembly.The lower ring has a flange portion which is attached to the insulatingring 246 by a plurality of screws 253. The spring members providecompliance between the wafer surface and the clamping plane when theclamp assembly engages the wafer. As best shown in FIG. 7, a section 255of the upper ring 251 is cut away over about at 170° arc to provideaccess for the wafer arm 80 to deposit wafers on the platen 194 when theclamp assembly is in its up or retracted position as shown in brokenline in FIG. 9.

A plurality (preferably three as shown in FIG. 8) of inwardly extendingprojections 256 are formed in the upper ring to engage a wafer forclamping to the platen surface. When the clamp is in its retractedposition and a wafer is inserted through the opening 255 by the arm 80the wafers are deposited on a set of projections extending inwardly fromthe upper ring below the opening, including pins 257 extending radiallyinward from the wall of upper ring and a finger 258 attached to theouter wall of the upper ring and extending upward into the opening anddefining a plane with the pins.

To provide sealing of the platen assembly when it is positioned at aprocess station O-rings 259 and 260 are received in grooves formed inthe face of the frame member 186. When the arm 80 is pivoted intoposition to place a wafer on the platen with clamp assembly in its upposition, the paddle 142 enters into the opening 255, the arm assemblyis lowered to deposit the wafer onto the pins 257 and finger 258, belowand the arm is pivoted to another position away from the platen. Fluidpressure is then applied to the cylinder 228 above the piston 232 tomove the piston downward, correspondingly moving the clamp assemblydownward to first deposit the wafer on the platen surface, then clamp itthereon. When the wafer is in place on the platen the platen assembly ispivoted upward to position the wafer in a vertical position at theopening of a desired processing station as illustrated in FIG. 11, whichfor purposes of illustration is shown as a sputtering station includinga sputter source 262.

ATMOSPHERIC CLAMP

In normal operation the platen rotary drive provides sufficient sealingforce between the platen assembly and the wall of the staging chamberwhen the platen assembly is rotated to its operating position facing aprocess chamber, as illustrated schematically in FIG. 11, since thepressure differential between the evacuated staging chamber and theevacuated process chamber is low. When, however, a process chamber isundergoing maintenance either in place or removed from the sputteringapparatus, and operations are to continue at other process stations, itis necessary to close the affected process station, using the platenassembly as a door or cutoff valve. In such instances there will beatmospheric pressure acting on the outside of the staging chamber, inwhich case it is considered necessary to provide additional closuremeans to maintain the vacuum integrity of the system.

Referring to FIG. 10, there is illustrated therein a pair of clampassemblies designated generally by the numeral 268, while FIG. 12 showsan enlarged view of one of the clamp assemblies. The assemblies areessentially identical and will be described interchangeably herein.

The clamp assemblies 268 are essentially toggle clamps which are capableof applying a relatively high closing force to the platen against thewall of the staging chamber. Each toggle mechanism comprises a link armmount 280 welded to the underside of a top wall member 281 of thestaging chamber, a lock arm 282 pivotally attached at one end to themount, and a connecting or toggle arm 284 pivotally attached to theopposite end of the lock arm, and to an actuating mechanism designatedgenerally by the numeral 286. A wedge-shaped clamp surface member 278(See FIG. 13) is attached to the back surface of the ring 170, androller bearing 287 mounted on the end of the lock arm 282 rides up thewedge 278 to transmit the clamping force of the toggle assembly to theplaten assembly and thus to side wall 60 of the staging chamber.

The actuating mechanism 286 comprises a mounting block 288 bolted towall 281, and a manually operated drive screw assembly 290. The drivescrew assembly 290 comprises a screw 292 extending through the mountingblock and having a link end 293 fixed to the lower end thereof forattachment to the connecting arm 284, a bearing 294 pressed into themounting block 288, a drive nut 295 threaded onto the screw and retainedto the bearing by a snap ring, a handle 296 pivotally attached to thedrive nut, and a vacuum bellows assembly 297 attached at its upper endto the mounting block and at its lower end to the link end 293.

The handle comprises a yoke 298 which fits over opposite flats of thenut and is pinned thereto, and a rod 300 fixed to the closed end of theyoke, the handle being capable of being flipped over 180° from theposition shown. The bellows assembly 297 comprises an upper flange 301clamped to the block 288, a lower flange 302 clamped to the link end 293and a metallic bellows 303 welded to the flanges. O-rings between theflanges and their associated mounting members maintain the vacuumintegrity of the clamp assembly.

Referring to FIG. 10, the right hand clamp assembly is shown in its openposition, and the left hand clamp is shown in its closed position. Theclamp assembly is moved from the open to the closed position by rotatingthe drive nut 295 with the handle assembly in a direction which willcause the screw to move downward. The downward movement of the screwcauses the lock arm 282 to move to the closed position, with theconnecting arm 284 acting as to toggle to lock the assembly in theclosed position.

OPERATION

Cassettes 28 of wafers 30 are initially deposited on the platform 26. Atthe commencement of a processing cycle wafers are transferred one-by-oneby the handling assembly 34 from the cassettes to the flat finder 32 andthen to a rack 41 positioned within one or the other of the load locks22. When the rack is fully loaded the lock is partially evacuated usingpumping means not shown, following which the corresponding plenum valve49 is opened and the load lock is evacuated to the desired level. Whenthe desired vacuum level is reached the heaters 45 are energized toeffect degassing of the batch of wafers. While the batch in the firstload lock is undergoing the degassing process the rack in the secondload lock 22 will have been positioned in the staging chamber 14 fortransfer one at a time to selected processing chambers.

When the degassing operation is complete the valve 49 in the first loadlock is closed and the elevator 47 is actuated to move the batch ofwafers from the load lock to the staging chamber 14, which is maintainedunder vacuum by a dedicated vacuum pump. At this time processing of thebatch originally in the second load lock will have been completed andthe processed wafers returned to the rack on the second elevator. Thesecond elevator is then actuated to return the batch of wafers to thesecond load lock, whereupon the second load lock is vented toatmosphere, and the wafers are returned to a cassette 28 by the pickingarm 37. A new batch of wafers is then loaded into the second load lockas described above where the evacuation and degassing processes arecarried out in preparation for further processing.

When the rack 41 is within the staging chamber 14, each of the wafersthereon is accessible by the wafer handling assembly 24. Referring toFIG. 1, if the wafer handling arm 80 of the handling assembly 24 is inthe position shown, and the left side rack as viewed in FIG. 2 ispositioned within the staging chamber, the arm 80 would first be rotatedclockwise (from the FIG. 1 position) until the paddle 142 is positionedopposite the rack. The arm 80 is then raised to position the paddle justbelow the level of the wafer to be processed, further clockwise to putthe paddle directly under the wafer, raised further to lift the waferoff the rack, and then rotated counterclockwise to extract the waferfrom the rack and lowered to a position suitable for accessing theindividual processing stations 16-19. When the wafer is extracted,proper positioning of the wafer on the paddle is verified by theproximity sensors 154.

Once the wafer is extracted and proper positioning verified the arm isrotated counterclockwise to position the paddle over the platen at adesired one of the processing stations 16-19. To accept a wafer from thepaddle, the platen assembly is put in its horizontal position as shownin FIG. 7, with the clamp assembly in its raised position as shown inFIG. 9. With the platen so positioned, the arm 80 is rotated until thepaddle enters the opening 255 and the wafer is centered over the platen194. The arm is then lowered to deposit the wafer on the two pins 257and third pin 258 and the arm is rotated to retract the paddle. Theclamp assembly is then moved downward to clamp the wafer against theplaten where it can then be preheated by contact with the platen, whichhas been preheated by the heating unit 209.

For processing, the platen assembly is rotated from the broken lineposition of FIG. 11 to the solid line position wherein the platenassembly sealingly engages a wall of the staging chamber adjacent to aprocessing chamber such as the sputtering chamber 18, whereupon thechamber 18 can be evacuated by its dedicated pumping system inpreparation for processing. Upon completion of processing the platenassembly is returned to its horizontal position and the clamp assemblyis positioned for extraction of the wafer by the arm 80. The wafer canthen be moved to another station for further processing, or ifprocessing is completed, returned to a rack 41 below one of the loadlocks from which they can then be returned to cassettes on the platform26 by means of the elevator 47 and the handling assembly 34. While theprocessing of one batch is being carried out, the second batch of waferscan be undergoing the degassing process.

It is important to note in considering the above sequence of events thatfrom the time the wafers are loaded onto the racks 41 until they arereturned to the cassettes after processing they are not subjected to anydirect radial movement. The arm 80 undergoes vertical (Z) and rotational(θ) motion only in transferring wafers between the racks and theplatens. This lack of radial motion greatly reduces the potential formisaligning the wafers in the transfer process and for generatingparticulates caused by relative motion between the wafers and thehandling components. The radial movement of the wafer which mightordinarily be required to inject the wafer into a processing chamber isaccomplished by the pivoting movement of the platen assembly which alsopermits the platen assembly to serve as a valve isolating the processstations from the staging chamber, and orients the wafers in the desiredvertical position for processing.

We claim:
 1. In a method for processing substrates, the steps of movingsubstrates into a first vacuum chamber to form a first batch ofsubstrates within said chamber, evacuating said first vacuum chamber toa subatmospheric pressure, heating said first batch of substrates toeffect degassing thereof within said first vacuum chamber, transferringsaid first batch of substrates as a unit from said first vacuum chamberto a transfer site within a second vacuum chamber, evacuating saidsecond vacuum chamber to a subatmospheric pressure, transferring saidsubstrates from said first batch at said transfer site one at a time toany one of a plurality of transfer stations within said second vacuumchamber, and then transferring a substrate from said one of a pluralityof transfer stations to a vacuum processing chamber adjacent thetransfer station.
 2. A method as claimed in claim 1, including the stepof simultaneously effecting vacuum isolation between said second vacuumchamber and said vacuum processing chamber when said substrate istransferred from said transfer station to said vacuum processingchamber.
 3. A method as claimed in claim 1 including providing anotherof said first vacuum chamber communicating with said second vacuumchamber in parallel with the first, moving substrates into said anotherof such first vacuum chamber to form a second batch of substrates,evacuating said another of said first vacuum chamber to a subatmosphericpressure, and heating said second batch of substrates to effectdegassing thereof; said evacuation of said another of said first vacuumchamber and said heating of said second batch being carried out whilethe steps commencing with the transfer of said first batch to saidsecond vacuum chamber are carried out.
 4. A method as claimed in claim3, including transferring said second batch of substrates as a unit fromsaid another of said first vacuum chamber to said transfer site withinsaid second vacuum chamber.
 5. A method as claimed in claim 1, whereinthe transfer of substrates from said batch to said transfer stations iseffected by moving a substrate through a first vertical movement torelease it from said batch, moving said substrate along a substantiallyconstant radius arcuate path between said transfer site and said any onetransfer station, and moving said substrate through a second verticalmovement to deposit it at said transfer station, said first and secondvertical movements and said movement along said arcuate path being theonly degrees of motion to which said substrates are subjected duringsaid transfer.
 6. A method as claimed in any one of claims 1, 3, 4 or 5,wherein said substrates are semiconductor wafers and are maintained in ahorizontal position during said steps of moving said substrates intosaid first vacuum chamber, transferring said batch of substrates fromsaid first vacuum chamber to said transfer site, and transferring saidsubstrates from said transfer site to said transfer station; and whereinsaid wafers are shifted from said horizontal positions to a verticalposition when they are transferred to a vacuum processing chamber. 7.Apparatus for processing substrates comprising a first vacuum chamber; asecond vacuum chamber communicating with said first vacuum chamber;means for selectively effecting vacuum isolation between said firstvacuum chamber and said second vacuum chamber; a plurality of thirdvacuum chambers each communicating with said second vacuum chamber;means for forming a batch of substrates within said first vacuumchamber; heating means within said first vacuum chamber operable todegas said batch of substrates; first transfer means operable totransfer said batch of substrates as a unit from said first vacuumchamber to a transfer site within said second vacuum chamber; aplurality of substrate transfer stations within said second vacuumchamber, each of said transfer stations being disposed adjacent one ofsaid third vacuum chambers; second transfer means operable to transfersubstrates one at a time between said transfer site and any one of saidtransfer stations and between one transfer station and any othertransfer station in random order; third transfer means operativelyassociated with each of said transfer stations and operable to transfera substrate from said transfer station to an adjacent third vacuumchamber and means associated with each of said transfer stations foreffecting vacuum isolation between said second vacuum chamber and athird vacuum chamber adjacent that transfer station.
 8. Apparatus asclaimed in claim 7, wherein said transfer stations are located on theperimeter of a circle, said transfer site is also disposed on saidperimeter, and said second substrate transfer means comprises an arm offixed length movable arcuately about a vertical axis, said arm includingsubstrate engaging means operable to engage and retain a substratethereon.
 9. Apparatus as claimed in claim 8, wherein said arm is alsomovable in a direction parallel to said vertical axis, the vertical andarcuate movements being the only degrees of movement to which said armand a substrate engaged thereby are subjected.
 10. Apparatus as claimedin claim 8, wherein said transfer site comprises first and secondtransfer locations disposed on said perimeter; said apparatus furtherincluding another of said first vacuum chamber communicating with saidsecond vacuum chamber, means for selectively effecting vacuum isolationbetween said another of said first vacuum chamber and said second vacuumchamber, means for forming a batch of substrates within said another ofsaid first vacuum chamber, heating means within said other first vacuumchamber operable to degas said batch of substrates therein, and anotherof said first transfer means operable to transfer a batch of substratesas a unit from said another of said first vacuum chamber to the secondtransfer location within said transfer site; said second transfer meansbeing operable to transfer substrates from either of said transferlocations.
 11. Apparatus as claimed in any one of claims 7, 8, 9, 10, inwhich each of said transfer stations comprises a substrate receivingplaten having a substrate support surface formed thereon, and said thirdtransfer means comprises means for moving said platen about a horizontalaxis between a first position wherein said substrate support surface isoriented horizontally within said second vacuum chamber and a secondposition wherein said substrate support surface is oriented verticallywithin one of said third vacuum chambers.
 12. Apparatus as claimed inclaim 11 in which said means for effecting vacuum isolation between atransfer station and an adjacent third vacuum chamber comprises sealmeans formed on said platen.